Passing Stars and Interstellar Speculations

by Paul Gilster on March 18, 2010

Watching how exoplanet news hits the press is always interesting, but I was surprised at how the discovery of CoRoT-9b (discussed here yesterday) was received. The scientific reward could be significant, which is why one scientist referred to the find as a ‘Rosetta stone,’ but the fact that we had a gas giant that was both analyzable through transits and not a ‘hot Jupiter’ evidently needed to be ginned up in some media circles. What emerged were headlines seeing similarities to our Solar System (New Exoplanet Like One of Ours) and making bizarre extrapolations: Corot-9b: Extra Solar Planet Proffers Hope of Inhabitation.

I suppose CoRoT-9b is like a planet in our Solar System in being a gas giant in a stable orbit not hugging its star, but it’s hardly alone in that regard. What makes it special is that we can study it both by radial velocity and transit methods, gaining insights into the composition of such ‘temperate’ gas giants. I suspect the headlines left many readers disappointed when they read the ensuing story and realized it wasn’t about a terrestrial world just like the Earth. As for colonizing a gas giant, well, I leave that to your imagination.

And what to do about Gliese 710? Here is a dwarf star that may, in approximately 1.5 million years, pass through the Oort Cloud, with all the disruptive effect that seems to describe. A rain of comets moving into the inner system? Headlines like Rogue Star to Hit the Solar System are lively, to be sure, and send a chill up the spine of that dedicated band that is convinced we’re all about to be destroyed by runaway celestial objects in 2012. News on a million-year time cycle is not something that sells papers, but ‘rogue stars’ just might.

As to Gl 710, Vadim Bobylev (Pulkovo Astronomical Observatory, St Petersburg) used revised Hipparcos data to make the call on its future near-miss. Looking at stars within 30 parsecs of the Sun, Bobylev found nine new candidates to add to previously known close encounters (the astronomer defines a ‘close encounter’ as passing less than 2 parsecs from the Sun). And here’s the scoop on the closest of these:

For the star GL 217.1, a well-known candidate for a passage close to the Sun, the new observational data were shown to change noticeably its previously known encounter parameters with the Sun. The encounter parameters found here are: dmin = 1.28 ± 0.06 pc and tmin = −(861 ± 40) thousand years. Improving the radial velocity for the white dwarf WD 0310–688 (HIP 14754) whose orbit passed at a distance dmin = 1.61 ± 0.19 pc from the solar orbit about 300 thousand years ago is of current interest. Our statistical simulations showed that the star GL 710 has not only a high probability of penetrating into the Oort cloud, P1 = 0.86, but also a nonzero probability, P2 = 1 × 10−4, of penetrating into the region where the influence of the passing star on Kuiper Belt objects is significant.

Gliese 710, then, may well penetrate the Oort Cloud, potentially causing the kind of disruption there that could bring comets into an Earth-crossing orbit. Of all the stars the astronomer studied, this is the only one with a high probability of entering the Oort region. Interestingly enough, apart from what Bobylev has given us, we know about 156 Hipparcos stars within a radius of 50 parsecs that either have or will encounter the Solar System within a distance of less than 5 parsecs in a window from 10 million years in the past to ten million years in the future. One revised study shows the frequency of encounters closer than one parsec to be roughly 11.7 events per million years (plus or minus 1.3).

A New Scientist article goes to work on the Gl 710 encounter (Hurtling Star on a Path to Clip Solar System), saying the star will almost certainly send comets toward the Earth, and speculating on possible changes to Neptune’s orbit, which could occur if the one in ten thousand probability of such a close penetration comes to pass. So Gl 710, now ‘hurtling’ 63 light years from us in the eastern part of the constallation Serpens, becomes an object of concern for our remote posterity.

Does interstellar travel occasionally get such nudges for those species fortunate enough to have the technology to exploit them? A star closing to these distances is potentially in range for a civilization able to make a 10,000 AU journey (roughly the distance between Proxima Centauri and Centauri A and B). It’s useful to remember that the vast distances between the stars are themselves changeable as the galaxy continues to evolve and as our Sun continues its passage around it. It’s also useful to keep a cosmic perspective, one that reckons that on a galactic scale, civilizations may find innumerable ways to spread.

If these encounters are as frequent as stated, the geological record would show whether we have previously had comets raining down on Earth and the other planets due to disturbances within the Oort cloud. Is there any evidence that this has occurred? If not, the composition of the Oort cloud may not be what we think.

In fact, Gl 710 is old news. As the abstract reports, the situation is “well-known.” Garcia-Sanchez published virtually the same finding with the old Hipparcos data in 2001 — cited therein. The 0.01% probability that Gl 710 will come within 1000 AUs of the sun hinges upon the margin of error of the measured proper motion of the star. When the J-MAPS mission reports new measurements of Gl 710’s position in 2016, the precision of its proper motion (derivable from a comparison with the Hipparcos position from 20 years earlier) will improve dramatically. ESA’s Gaia will improve that figure even more dramatically when that catalog is published in 2020. Then we will be able to constrain the breadth of the window of Gl 710’s passing to much better precision.

Of much more scientific interest would be to find nearby low proper motion stars with positive radial velocities (redshift) — which means the passing occurred in the past — potentially coinciding with some event discoverable in the Earth’s geological record. Bobylev’s study is by no means exhaustive.

P.S.. “Does interstellar travel occasionally get such nudges for those species fortunate enough to have the technology to exploit them?”

Fritz Zwicky once proposed that if some technology could be devised to interfere with the physics of the sun so that it preferentially radiated in some preferred direction, then we could could propel the whole solar system like a starship. Always one to think outside the box, Zwicky was.

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Does interstellar travel occasionally get such nudges for those species fortunate enough to have the technology to exploit them?
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I may be stating the obvious here, but that nudge may come in more than just one form. If a species is using solar sails to cross interstellar distances then they might not just colonize the passing star and wait for the next one to pass by. They might do a close pass by their own star and then do a close pass of the passing star, getting a boost for further distances. They might even cycle between the stars getting a number of such close passes depending on the gravity of the star and the speed of their vessel. I wonder, just how fast would an object have to be going before it’s going too fast to be able to slingshot around a star like the sun, and just how much extra speed could it pick up?

The possibility of Gl710 coming close to the Sun isn’t a new finding, as the study’s author notes. What the new study does is quantify the probabilities based on more recent information about the motions and distances of the stars. Quite surprisingly high probabilities for a near pass for a star so far away. Question for coming centuries is just how close will it come.

Incidentally J.B.S. Haldane speculated about using stellar close-calls to star-hop in his SF piece “The Last Judgement” – a retrospective tale written by a Venusian colonist after Earth is destroyed by the Moon c.3 million AD. The Venusians use solar-sails and are planning a star-hop when Sol nears a cluster. Or some such – been 20 years since I read it.

If our Oort Cloud extends a light year or more from Sol and the Alpha Centaurian cloud is of similar dimension, are they already interacting?

Is WISE able to detect Oort clouds of nearby stars, if they exist that is?

Starships ? of course! But, perhaps a viable sequence is stepwise through our own cloud and onward to the AC cloud by hopping a trans-solar sytem comet? Afterall, this blog is about dreams.

Is there a way to estimate the numbers of deep space interstellar comets that have been nudged away from their home stars? I wonder what fraction of our familiar comets are actually captured interloppers?

Thanks for clarification of the significance of this new “Rosetta Stone”. A true breakthrough.

@Erik A: Many years ago now, I remember a NOVA episode that correlated mass extinctions with a regular 65 my cycle, suggesting that comets were somehow being sent earthward by a periodic disturbance. I think they even mentioned Nemesis on that show

Also, what would a Zwicky star propulsion system at speed look like? A doppler shifted Dyson sphere with a hole in it?

So… The earth is could actually be going through a quiet period (comparatively) and it is in this low activity period that civilization has formed…(I include all civilizations throughout the history of man as one civilization) it seems like this may be our window of opportunity that could be wasted if we do not act on it… This cosmological violence may be common enough throughout our galaxy that it may explain the absence of large discernible artifacts from super-civilizations… Meaning that the chaos in our galaxy leaves very little time if a civilization doesn’t become aware of the danger in a timely manner.

if these close encounters are so frequent and violent, and even if they are not, a civilisation would be wise to consider developing a respawning technology. in the same way that all living instances of insects or bacteria in an ecosystem might be wiped out, but their hardy eggs or spores survive until safer times when a new generation can be reborn – a technologically advanced civilisation could build respawning facilities around a planet or in the solar system. in the event of a nuclear holocaust or meteorite strike, an AI custodian of such facilities could wait for however long it takes for the biosphere to once again become reinhabitable, before releasing cloned humans and animals to repopulate the planet – like a futuristic noah’s ark

in the quest to make humanity survive and thrive in the cosmos, this kind of backup system may well come as a precursor to us being able to colonise other solar systems

going back to Gliese 710, an AI somewhere in the solar system could be set to prepare a human/earthlife colonisation starhopping mission for its encounter with our solar system in 1.5 million years.

in the quest to make humanity survive and thrive in the cosmos, this kind of backup system may well come as a precursor to us being able to colonise other solar systems

Indeed, given the existence of such “arks”, it would be a small step to build some more and send them off to a long, slow, interstellar journey to eventually reach other star systems and do the same as they would do here.

Alternatively, we could construct self replicating Arks. I am talking, of course, about space colonies… such an effort is closer to our current technological capability, and we get a lot more benefit as well.

Indeed, I imagine most if not all self replicating starships are going to be crewed, if not outright bioships – imagine a Dyson Tree propelled by a fusion drive burning deuterium, with massive starlight collectors focusing the dim starlight on the ultra-efficient leaves. Hopefully we’ll be able to engineer the being so that the light concentrators are grown, rather than manufacture… the seed of such a plant could be fired towards a star system in great number, so that by the time the humans follow up there are already a few colonies.

Alternatively, long lived humans may make short hops between brown dwarfs in such ships, each journey lasting perhaps 30 years and using up their deuterium supply in the process (they’ll have stripped out unneeded ices long ago). If P-P fusion works out…

I’m new to the idea of a dyson tree, just wiki’d it – very interesting – I’m guessing that biotechnology and genetic engineering is going to be completely revolutionary to many things over the coming decades, including space.

So perhaps a dyson tree organism would be a biology-computer synthesis, a biological organism controlled by very advanced computer, either with human or AI control.

Before even interstellar travel, it would be fascinating if comets throughout our solar sytem could become inhabited by human-designed plant-machines. Some could prepare the comets for human habitation, others could form a network of probes/telescopes through the solar system

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This is less than 0.005 c, so it is not much if you are in a hurry.
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That is depressingly low. On the other hand if you’re willing to wait
a few hundred thousand years for a star to pass close by then you
probably aren’t in that great of a rush. Might be good for getting
very large masses, like worldships, up to speed.

Charter

In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For the last seven years, this site has coordinated its efforts with the Tau Zero Foundation, and now serves as the Foundation's news forum. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image: Marco Lorenzi).

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